Most modern baseball and softball bats are typically made from aluminum, aluminum alloys, composite materials, or a combination of such materials. Bats are tubular and hollow in order to meet the weight requirements of the end user and typically have a barrel portion, a handle portion, and a tapered mid-section portion connecting the handle and barrel portions. During game play, as a pitcher throws the ball with high velocity, the batter attempts to hit the ball with the bat. Upon impact between the ball and the bat, a significant amount of the kinetic energy from the ball is transferred to the bat. The bat absorbs most of the energy, and as the ball's direction changes in response to the collision, some of the energy from the bat is transferred to the ball. Both the ball and the bat deform in response to the collision. The result is that the exit speed, the speed at which the ball leaves the bat, is usually much greater than the speed at which the ball was thrown.
A batter generally prefers a higher exit speed because it allows the ball to travel farther and it also allows the ball to get past the infield defenders before they can move to a position to intercept the ball. A ball that has an exit speed that is too high may reach the player before the player has a chance to react to either catch the ball or get out of the way. The defenders that are closer to the batter, such as the infield defenders and the pitcher especially, are at risk for being struck by a batted ball that travels at a velocity that exceeds the defender's ability to react to the hit. Consequently, there are sport governing bodies that have created and promulgated regulations to improve the safety of the sport for all of its players. One of the regulations limits the bat-ball coefficient of restitution, or BBCOR, which is a measure of bat performance by using the inbound and rebound speeds of the ball to calculate the energy transfer efficiency of the bat. This is often described as measuring the bat's “trampoline effect” or the bat's elasticity. By limiting the bat's performance, it is believed that the game will be safer for all players. There have been several approaches used for limiting a bat's performance. Some approaches reduce bat performance by stiffening the bat so that its trampoline effect is reduced.
The bat stiffening is often achieved by adding inserts to the bat to create doable walled or walled bats that utilize a secondary or tertiary tubular members that are coaxial with the barrel. Some of these multi-walled bats apply the multi-walls along the entire length of the barrel, while others only add the additional walls at preselected positions along the barrel. Other approaches are aimed at stiffening the bates sweet spot in a radial direction by providing increased thickness of the barrel at the sweet spot location. H -ever, all the approaches suffer from from one or more drawbacks. For example, many of the approaches reduce the bat efficiency for all combinations of bat/ball collision speeds. The result is that a slower bat/ball speed will produce a correspondingly slower exit speed. Furthermore, because most bats have cylindrical grips and can be held in any rotational orientation, the bat needs to have consistent hitting characteristics around the entire circumference of the bat. It is very difficult to control manufacturing tolerances to the extent necessary to ensure that a bat has a consistent hitting profile around its entire periphery. When utilizing concentric tubular members for example, minute variances in surface smoothness, ovality, straightness, concentricity, and rail thickness all compound to produce significant variability in the ba s performance along its length and at various locations around its circumference. It would be a significant improvemement in the art for a bat to perform non-linearly with respect to bat/ball collision speeds, and to attenuate the BBCOR as speeds approach the promulgated industry standards. It would also be a major improvement if a bat could be manufactured to produce consistent hitting properties at its sweet spot. It would be a further advantage if the features used for attenuating performance could be positioned in a way to give increased accuracy, thereby limiting bat-to-bat variation, and permitting less margin of error to the performance limits,